Engines for handheld working tools are often of the two-stroke type and very compactly designed, because the tool should naturally be as light and compact as possible. This aim permeates the design of all of the tool's components, including the cylinder's. Thus, cylinders for portable working tools, such as chain saws, have as a rule a very simple and compact design. This simplicity leads to a compact design and low production costs. At the same time it also leads to a fuel consumption and to exhaust emissions, which leaves a deal to be desired, especially as the requirements for low exhaust emissions gradually increase.